The present invention relates to a sheet feeding apparatus to separate and feed individual sheets in a sheet storage device, and more particularly to a sheet feeding apparatus which is of the type that intermittently and separately supplies sheets from a storage device through a semicylindrical pickup roller to office automation equipment such as a printer.
An important problem in the sheet feeding art relates to stable and accurate feeding of sheets from a sheet storage device to equipment. Here, a description will be made with reference to FIGS. 13 to 16 in terms of an arrangement of a conventional sheet feeding apparatus and a problem inherent to such a conventional sheet feeding apparatus. In FIGS. 13 and 14, in response to setting a sheet-loaded sheet storage device 121 to a body of a laser printer 111, a sheet feeding apparatus, designated at numeral 141, supplies the laser printer 111 with sheets 123 pushed up by a push-up spring 122. The sheet feeding apparatus 141 comprises a semicylindrical pickup roller 144 coaxially fixed to a drive shaft 142, a stopping roller 147 disposed at both end portions (sides) of the semicylindrical pickup roller 144 and coaxially and rotatably couped to the drive shaft 142, a retard pad 146 disposed to be elastically brought into contact with the circumference of the semicylindrical pickup roller 144 by means of elastic members (springs) 145, and a sheet guide plate 148 for rotatably supporting the retard pad 146 to guide the sheets 123. The sheets 123 fed from the sheet feeding apparatus 141 are supplied through a carrying roller 149 into the body of the laser printer 111.
FIG. 15 is a cross-sectional illustration of the semicylindrical pickup roller 144 taken along a line X--X in FIG. 14. In FIG. 15, the semicylindrical pickup roller 144, being made of a rubber, is arranged to have a diameter slightly greater than the diameter of the stopping roller 147 and fixedly coupled through a core member 143 to the drive shaft 142. Further, the semicylindrical pickup roller 144 has a plurality of grooves 144a formed along its axis and has a notch 144c.
In operation, the sheets 123 placed in the sheet storage device 121, as mentioned above, are pushed up by the push-up spring 122 to be pressed against the stopping roller 147 whereby the sheets 123 are positioned for supply. Then, the semicylindrical pickup roller 144 is rotated by one revolution in a direction indicated by an arrow in FIG. 13, whereby a leading portion 144b of the semicylindrical pickup roller 144 comes into contact with a front portion of the uppermost (topmost) sheet 123 so that the uppermost sheet 123 is moved forwardly by means of a frictional force relative to the semicylindrical pickup roller 144. At this time, the retard pad 146 comes into contact with the sheets 123 other than the uppermost sheet 123 to suppress the supply of the sheets 123 by means of a sliding resistance to prevent the following sheets 123 from being supplied simultaneously with the uppermost sheet 123.
There is a problem which arises with such a sheet feeding apparatus, however, in that, in cases where the rigidity of the sheets 123 is low, when the second sheet 123 follows the uppermost sheet 123 moved forwardly by the semicylindrical pickup roller 144, the second sheet floats or rises as illustrated in FIG. 16 whereby the aforementioned sliding resistance between the retard pad 146 and the sheet 123 becomes low, that is, the retard pad 146 does not fulfil its function, to result in allowing the simultaneous supply of the more than one sheet 123.